1. Field of the Invention
The present invention relates to an anode having an anode current collector and an anode active material layer, and a battery using it.
2. Description of the Related Art
In recent years, in connection with high-performance and multi-function of mobile devices, high capacities of secondary batteries, the power source for the mobile devices have been desired earnestly. As a secondary battery which meets this demand, there is a lithium secondary battery. However, in the case of using cobalt acid lithium for a cathode and graphite for an anode, which is currently a typical form for lithium secondary batteries, the battery capacity is in a saturated state, and it is extremely difficult to greatly obtain a high capacity of the battery. Therefore, from old times, using metal lithium (Li) for an anode has been considered. However, in order to put the anode to practical use, it is necessary to improve efficiency of precipitation dissolution of lithium and to control dendrite precipitation form.
Meanwhile, a high capacity anode using silicon (Si), tin (Sn) or the like has been actively considered. However, when charge and discharge are repeated, shapes of these anodes are collapsed due to significant expansion and shrinkage of an anode active material, current collecting characteristics are lowered, and dissolution reaction of an electrolyte is promoted due to an increased superficial area, so that their cycle characteristics are extremely poor. Therefore, an anode wherein an anode active material layer is formed on an anode current collector by vapor-phase deposition method, liquid-phase deposition method, sintering method or the like has been considered (for example, refer to Japanese Unexamined Patent Application Publication No. H08-50922, Japanese Patent Publication No. 2948205, and Japanese Unexamined Patent Application Publication No. H11-135115). Specially, an anode wherein this anode is further provided with heat treatment to alloy at least on a part of an interface between the anode active material layer and the anode current collector has attracted attention as an anode providing high characteristics. According to this anode, since miniaturization can be inhibited compared to conventional coating type anodes wherein slurry containing a particulate anode active material, a binder and the like are applied, and the anode current collector and the anode active material layer can be integrated, electronic conduction in the anode becomes extremely excellent, and high performance in terms of capacity and cycle life is expected. In addition, a conductive agent, a binder, voids and the like which have existed in the anode conventionally can be reduced or excluded. Therefore, the anode can become a thin film essentially.
However, even when using this anode, there has been a problem that a shape of the anode active material layer is collapsed due to charge and discharge, a side reaction with the electrolyte in accordance with the collapse is raised, and the battery capacity is reduced as charge and discharge are repeated.